Fig. 7. Functional study and summary of progenitor topology in the regulation of feather lengths.

(A and B) Disruption of Notch signaling by misexpression NICD shows short feather filaments. (C to F′) Comparison of H&E, PCNA, and YAP1 staining between control and RCAS-NICD–infected samples. Note the precocious barb ridge formation (C′) and the lack of PCNA-positive cells in the epidermis (D′) (pink arrow). RCAS-NICD samples show the disappearance of YAP1 in the epidermis (E′) (red arrow) but a paradoxical increase in YAP1 in the PP. (G and H) Inhibition of YAP activity converts the tapering feather filament into short, stubby, cylindrical filaments. (I to L′) Comparison of control and RCAS-dnYAP1–infected samples. Note the reduced thickness of TA cell zone (J′) (white arrow) and intermediate layer (K′) (green arrow). There are large numbers of NOTCH1-positive PP cells. The distal end fails to form barb branches. (M and N) Inhibition of WNT signaling by RCAS-WIF1 reduces feather length. (O to R′) Comparison of control and RCAS-WIF1–infected samples. Note the reduced feather follicle width (O′), the reduction of PCNA-positive cells in the epidermis (P′) (yellow arrow), and reduced YAP1 expression (Q′) (blue arrow). (S) Table summarizing the findings using RCAS-mediated gene misexpression. (T) Model of YAP1 interacted with the DLL/NOTCH pathway regulating feather length by fine-tuning the progenitor cell topology. Compared to short feathers, long feathers have a bigger stem cell zone marked by DLL1 expression (red color). The Phoenix chicken main sickle feathers have an elongated stem cell zone and higher YAP1 activity that may contribute to the longer growth period. Left: Schematic drawing of a feather follicle. For [(B), (H), and (N)], five flight feather filaments from the right (experiment) and left (control) wings were measured. ***P < 0.001.